LC trick to parse number from a list of characters

 Lets say you have a string "leet23code" and you want to parse the characters as number 23, and you are not allowed to typecast after collecting the complete number "23" as string.

Its not really a trick but its just a nice way to build the number from string. 

The obvious way to do this is by multiplying the position of digit in number and adding it, for example 23 can be represented as

(2 * 10 ^ 1 ) + (3 * 10 ^ 0)

we would need to keep track of the power of 10 to build the number

something like

power = 0

my_number = 0

for c in s:

if c.isnumeric():

my_number += int(c) + 10 * power

power += 1

 This is  nice and easy to  understand, but there is even a better trick than this

def parse_number(self, s):

my_number = 0

for c in s:

if c.isnumeric():

my_number = my_number * 10 + int(c)

return my_number

 This reduces the need for keeping track of power, because we knew power is incremented every time.